For high-speed synchronous motors, many types of motor control technologies have been adopted. Vector control is an accurate method of synchronous motor operation. Such a control system, however, is computationally intensive. A vector control method typically maps three-phase motor voltages and currents into a two-axis system. To accomplish this mapping, the vector control system requires precise rotor information, for example, rotor angular position and speed. Traditionally, feedback devices, such as resolvers, encoders or Hall Effect sensors, have been used to provide motor speed and rotor position information to the motor controller for motor control.
Recently, many types of turbo machinery have adapted high-speed synchronous motors as a power source. These types of machines may operate at rotational speeds of 150 krpm and beyond. It is very difficult to find feedback devices or sensors for such high operating speeds. Sensors that currently exist for such high speed turbo machines tend to be expensive and have low reliability. In addition, existing position sensors often limit system configuration options. These factors become prohibitive in high volume applications, such as for control systems used in industrial turbo-blowers and turbo-compressors.
If position sensors could be eliminated from a control system for a high-speed turbo machinery synchronous motor without affecting operation and efficiency of the motor and the turbo machine in which it is used, manufacturing costs could be significantly reduced while the reliability of the motor could be improved. Position-sensorless control can obtain rotor information from the electromagnetic characteristics of the synchronous motor and thus eliminate the need for a feedback sensor. Various position-sensorless vector control schemes already exist which may accomplish the task. These can be acquired from various vendors in application notes or through other means. However, existing methods are limited in various abilities.
For example, some common limitations on existing position-sensorless control schemes include: some control methods are not able to maintain control at extremely high speeds; and some control methods are limited in responsiveness to changes in load, torque and commanded speed. In addition, some controller configurations are limited in power and thus are not useful in certain applications like high-speed turbo machinery. Moreover, components and methods that are successful in lower power applications are often not relevant to all varieties of synchronous motors, especially high speed motors. For these reasons, an improved control method, specifically for use in turbo-machinery operating at high speeds, is necessary.
The proposed position-sensorless control system and method of operation for a synchronous motor in accordance with the present invention avoids the drawbacks common to existing control systems and position-sensorless control systems, such as those discussed above, by using position and velocity estimation. The proposed position-sensorless control system can be used in turbo machinery operating at extremely high speeds without affecting the operation and efficiency of the synchronous motor. The present position-sensorless control system can accommodate such high speeds while also having the ability to respond to changes in load, torque, and commanded speed, all while improving system reliability.